1. Field of Invention
This invention relates to apparatus for compressing and conveying gases, and with regard to certain more specific features, to apparatus which are used as compressors in refrigeration and air-conditioning equipment.
2. Description of Prior Art
Since the introduction of vapor-compression technology, a need has existed for more efficient compressors. This need has never been more apparent than today. Due to production cut backs of CFC refrigerants which damage the ozone layer, there will be an increasing reliance on "safer" but less efficient refrigerants. These refrigerants which have lower coefficients of performance, will make it difficult for current compressor technology to keep pace with the increasing efficiency demands of energy conservation. Consequently, there is a need for more efficient refrigeration compressors to offset the resulting increase in national energy consumption.
Heretofore, refrigeration and air-conditioning compressors, which were used in vapor-compression type refrigeration equipment, required many moving parts. Reciprocating, rotary, and centrifugal compressors, which are now commonly used for refrigeration applications, all have numerous moving parts. Each of these compressors will consume a portion of energy which serves only to move its parts against their frictional forces, as well as to overcome their inertia. This energy is lost in overcoming the mechanical friction and inertia of the parts, and cannot contribute to the actual work of gas compression. Therefore, the compressor's efficiency suffers. Moving parts also reduce dependability and increase the cost of operation, since they are subject to mechanical failure and fatigue. Consequently, both the failure rate and the energy consumption of a compressor tend to increase as the number of moving parts increases.
Typical refrigeration and air-conditioning compressors must use oils to reduce the friction and wear of moving parts. The presence of oils in contemporary compressors presents certain difficulties. Compressors which need oil for their operation will allow this oil to mix with the refrigerant. The circulation of this oil through the refrigeration cycle will lower the system's overall coefficient of performance, thus increasing the system's energy consumption. Another disadvantage of oil-refrigerant mixtures relates to the development of new refrigerants. It is hoped that non-ozone depleting refrigerants will be developed to replace the CFC family of refrigerants. For a new refrigerant to be considered successful, it must be compatible with compressor oils. Oil compatibility is the subject of performance and toxicity tests which could add long delays to the release of new refrigerants. Hence, the presence of oils in refrigeration and air-conditioning compressors, reduces system efficiency and slows the development of new refrigerants.
For pumps in general, much effort has been exerted to achieve designs which lack these traditional moving parts and their associated disadvantages. Some of these efforts have produced pumps which seek to operate directly on the pumped medium, using non-mechanical means. Typically these pumps operate by pressurizing the pumped medium using heat. The patent literature contains many examples of these methods. One such example is shown in U.S. Pat. No. 3,898,017 to Mandroian, Aug. 5, 1975. Therein is disclosed a chamber in which a gas is heated and subsequently expelled through an egress means. As the chamber's remaining gas cools the resulting pressure differential causes more gas to be drawn into the chamber through an ingress means. This same method is employed in U.S. Pat. No. 3,397,648 to Henderson, Aug. 20, 1968.
This method of pumping as described in the above patents may work for low pressure differentials, low volume, and slow pumping cycles. However, these pumps would clearly be inadequate were they to be employed as refrigeration compressors. This inadequacy can be seen by examining the ideal gas equation, PV=nRT. This equation shows that if a constant volume of gas is to be pressurized by heat alone, then to increase the pressure by a factor of "m", you must increase the temperature by a factor of "m." Thus, to obtain the pressure differentials needed in vapor-compression equipment, the refrigerant would have to be heated to extremely high temperatures. For example, a typical an R-12 refrigeration cycle with a 20.degree. F. evaporator, needs approximately a 3.7 factor gain in pressure from evaporator to condenser. Assuming a superheated vapor of 70.degree. F. arrives at the compressor, to increase the pressure by a factor of 3.7 would require heating the refrigerant to a temperature in excess of 1500.degree. F. Such high temperatures could ionize or possibly disassociate the refrigerant.
Seldom have any of the above mentioned pumping methods been applied to the field of refrigeration. One such attempt is seen in U.S. Pat. No. 2,050,391 to Spencer, Aug. 11, 1936. In the Spencer patent, a chamber is provided in which a gas is heated by spark discharge and subsequently expelled through an egress means, due to the resulting pressure increase. As the chamber's remaining gas cools, the resulting pressure differential causes more gas to be drawn into the chamber through an ingress means. This approach results in ionization of the refrigerant, and could cause highly undesirable chemical reactions within the refrigeration equipment. For a practical refrigeration system, such chemical reactions would be quite unsatisfactory.
It is apparent that oil-free refrigeration and air-conditioning compressors, which require few moving parts, have not been satisfactorily developed. It is also apparent that if such compressors were available, they could simplify the development of new refrigerants, and offer improved dependability and efficiency, thereby reducing energy consumption.